Hepatitis C virus (HCV) infection is a major health problem that leads to chronic liver disease, such as cirrhosis and hepatocellular carcinoma, in a substantial number of infected individuals, estimated to be 2-15% of the world's population. There are over 3 million chronically infected people in the United States alone, according to the U.S. Center for Disease Control. About 150 million individuals are chronically infected worldwide, with at least 3 to 4 million people being infected each year. Hepatitis C Fact Sheet, World Health Organization, July 2012. Once infected, about 20% of people clear the virus, but the rest harbor HCV the rest of their lives. Ten to twenty percent of chronically infected individuals eventually develop liver-destroying cirrhosis or cancer. HCV is transmitted parenterally by contaminated blood and blood products, contaminated needles, or sexually and vertically from infected mothers or carrier mothers to their off-spring.
Different approaches to HCV therapy have been taken, which include the inhibition of viral serine proteinase (NS3 protease), helicase, and RNA-dependent RNA polymerase (NS5B), and the development of a vaccine. Current and investigational treatments for HCV infection are reviewed in Poordad et al., Treating hepatitis C: current standard of care and emerging direct-acting antiviral agents. Journal of Viral Hepatitis 19: 449-464 (2012); and G. J. Dore, The changing therapeutic landscape for hepatitis C. Med. J. Australia 196: 629-632 (2012). Despite the availability of therapeutic treatment options, chronic HCV infection remains a major healthcare concern. Moreover, there is no established vaccine for HCV. Consequently, there is a need for improved therapeutic agents that effectively combat chronic HCV infection.
The HCV virion is an enveloped positive-strand RNA virus with a single oligoribonucleotide genomic sequence of about 9400 bases which encodes a polyprotein of about 3,000 amino acids. The protein products of the HCV gene consist of the structural proteins C, E1, and E2, and the non-structural proteins NS2, NS3, NS4A, NS4B, NS5A and NS5B. The nonstructural (NS) proteins are believed to provide the catalytic machinery for viral replication.
HCV NS5A is a 447 amino acid phosphoprotein which lacks a defined enzymatic function. The NS5A protein is either 56 kd or 58 kd, depending on its phosphorylation state (Tanji, et al. J. Virol. 69:3980-3986 (1995)). HCV NS5A resides in a replication complex and may be responsible for the switch from replication of RNA to production of infectious virus (Huang, Y, et al., Virology 364:1-9 (2007)).
Multicyclic HCV NS5A inhibitors have been reported. See U.S. Patent Publication Nos. US20080311075, US20080044379, US20080050336, US20080044380, US20090202483 and US2009020478. HCV NS5A inhibitors having fused tricyclic moieties are disclosed in International Patent Publication Nos. WO 10/065681, WO 10/065668, and WO 10/065674.
Other HCV NS5A inhibitors and their use for reducing viral load in HCV infected humans have been described in U.S. Patent Publication No. US20060276511.